Combined moving coil loudspeaker and transformer



Aug. 9,1949. J. JLYROOT 2,478,642 I COMBINED MOVING con. LOUDSPEAKER ANDTRANSFORMER Filed 001:. 9, 1946 F1. E- J J 43 /J 53 34 I 1 3 3 IAZYURIYEY Patented Aug. 9, 1949 John-J: Root, NewYorli NLY'.Apiii'itatitn downer-'9, 194%? serisr'rte 'mz-izta partofmfy 9310a;fired June 25 ii I anciesea loud 1p design as to be of a d What ii tne'oi eraii I g e s aner was subsan any deterfaiged tithe erect its ainstantinvent'idri mearp es oi't'lie advantages prior application; anfurther princi s to entering coil type-or ti re i s lecti od spalfi. x gp r T prior t pes; of iiioviiigf coi driving" spe wit; the was" gneiaumspcsea at the so orafii bhi'fid the'cone. Bent arcane the g fu therrarwa Iy'was either using orapo fizng neat 'ifia gnt arrangement. Anofitut t n's former was generally mounted on the framewof'li iii orderto match the impedance of the voice coil to theoutput circuit to whichthe speaker was contacted. h h

The preseat intentiii turmerares possible the mounting of thematchiag'transrormerso that the overallspaeerequirements of the loudspeaker are minimized. A

tfii-objects of my invention will be, anagram thei'jllowingdescriptionit being" un er- Etiiod that the above general statements ofthe objects of myinvention are intended to describe and not limit it anymanner.

' :;l e cross sectional new iii 'a lodd speaker "'c'b stfiicteii'inaccordanee tvith 'tlie principles of the invention, and taken acrossline 22 of Fig. 1.

Fig. 2 is a top view thereof.

The speaker assembly comprises a cone diaphragm II) which may befabricated of stiff paper or any other non-magnetic material havingSuite able acoustical properties. Diagram H] is formed with conventionalcorrugations H and is secured around its periphery l2 to an annularbracket member l3.

Bracket member I3 is connected at spaced points thereof as by screws l4to an annular casing wall l5 having an integral depending flange l6.Casing wall l5 as well as flange l6 function as a portion of theferromagnetic circuit and are therefore made of steel or equivalentferromagnetic substance. The casing further comprises the annular floorI1 formed with an integral reene e i the deter or t-h seniors:- (01.mow-1:15am

trant columrrl a'f whiclig, co operation with flange l 6,provides-amelectromagnetic: aireap? asrwilUiQ herernaftadescribedr Mm"tamed: betweenlwall t5 fltiol fl boltsgnotshown, is; anon? ntiiarpeflnarient mag-iiet B9 for supplying a poijarizing nelatotneunit, v

we phragmiltkis connected as by a; suitable adhesive an annular, hlzeeiitensioni 20 whieliramay: be offinsulatin m Ma l. sucneoane tio is:fliected: substmr t y mater-it to the peripheral portion. of: thecortical area; rror the -diaphragm Wort. as Othell-v wise stated;massacre-the periphery or brim. of the diaphragm as represented by theedgepob tioii more the corrugations Secured in a coir analliner toftneextension 20 is; the moving or voice coil 22' so that it is: concentricivi the aitis of the diaphragm and disposed within the-electromagneticair gap produced by the'fiahge Tia-rid ieiitrant column IE.

' asiiig wan lie-rid new IT; as spaced-by the permanent magnet t9,define an annular chamher in which is disposed the annular outputtransformer Tra'nSformer "23 comprises a primary winding having leads 25and 26 and a secondary winding 21 having leads 2! and 2!.

is conventional, leads 2'8 and 29 of the secondary winding are.connected to the voice coil 22 which isthereupoh'provi'ded with audiocurrents so as to produce a magnetic field. In the instant'erribodiinent'such connection is effected through the rivet 3'0 and lug3| to which both one voice eouiead and secondary winding lead '29 areadhered, similar connection for the other voice coil lead is effectedthrough the rivet 32 and soldering lug 33; It will beirecognized thatthe "construction "of "transformer 23 is Sikh as vto produce a steppeddown secondary windingfl to match the impedance of the voice coil 22.Transformer leads 25, 26, 28 and 29 may emerge from suitable openings 34and 35 formed in the floor H.

To operate the loud speaker from a vacuum tube amplifier, leads 25 and26 are directly connected to the plate of the final power tube of theamplifier and the positive plate voltage terminal, respectively. In theabsence of an audio signal from the power tube, the permanent magnet I9polarizes flange I6 and column l8 north and south, respectively, so asto establish a constant field in the air gap formed between them. Uponthe introduction of an audio signal to the amplifier, an alternatingcurrent component corresponding to the signal appears in the output ofthe power tube. The resultant current which flows through the voice coil22 produces a magnetic field which interacts with the polarizing orconstant magnetic field to produce a force which moves the coil parallelto the axis of the diaphragm II]. This produces the required vibrationor movement which generates sound waves.

It is to be observed that by driving diaphragm ID at its peripheral areaand by disposing the voice coil thereat, a substantial reduction is madepossible in the spaceoccupied by the speaker assembly.' This objectiveis further contributed to by the disposition of the output transformerwhich, in distinction to conventional dispositions thereof, does not jutout from'the, main body of the speaker. The magnetic structure of thespeaker is built away from the central area of the diaphragm so as topermit the formation of a cone thereat. transformer laterally surroundthe conical area, the depth of the motor assembly being substantiallyequivalent to the height of the conical central area so that it'isdisposed in'a plane defined by the height of the conical area.

Thus, there has been'shown what at present is considered a preferredembodiment of the invention. It will be apparent, however, that manychanges and modifications are possible without departing from the spiritthereof. For example, vwherethepower tube-of the amplifier is drawing'ahigh value of current,- the primary Winding-24 may be relied upon tosupply a polarizing'source as described in myprior above mentionedapplication. In this event, the permanent magnet [9 would. beunnecessary.

-Iclaim:, r 1. An'electroacoustic transducer comprisingin combinationanacoustical diaphragm having a conical central area, a voice'coil mountedadjacent to the periphery of said diaphragm so as to permit said conicalcentral area to vibrate freely, and electromagnetic pole means ofannular form disposed in operativerelation to said voice coil adjacentthe periphery of said diaphragm whereby the apex of said conical area isunobstructed thereby, said electrical pole means forming a chamber, andan annular transformer for supplying audio signals disposed within saidchamber and electrically connected to said voice coil.

2. An article according to claim 1 wherein said chamber is of a depthsubstantially equal to the height of the conical central area and issubstantially disposed in a plane defined by said height.

3. An article according to claiml including a permanent magnet ofannular form for supplying a polarizing force tosaid voice coil, saidpermanent magnet'being disposed adjacent the periphery of saiddiaphragm, and substantially in the plane of said chamber.

The magnetic structure and 4. An electroacoustic transducer comprising acombination an acoustical diaphragm having a conical central area, avoice coil mounted adjacent to the periphery of said diaphragm so as topermit said conical central area to vibrate freely, electromagnetic polemeans of annular form disposed in operative relation to said voice coiladjacent the periphery of said diaphragm whereby the "apex of.saidiconical area is unobstructed thereby, a permanent magnet forsupplying a polarizing force to said voice coil,

' said electromagnetic pole means and permanent magnet forming a chamberlaterally surrounding said conical central area, said chamber being of adepth substantially equal to the height of the'conical central area soas to be disposed in -a plane substantially defined by the heightthereof, and an annular transformer for supplying audio signals disposedwithin said chamber and electrically connected to said voice coil.

. 5. An electroacoustic transducer comprising in combination anacoustical diaphragm having a central area and a brim integraltherewith, an annular extension formed on said diaphragm adjacent saidbrim, a voice coil wound around said extension so as to be disposedadjacent the periphery of said diaphragm and so as to leave the centralarea of said diaphragm free to vibrate, electromagnetic pole means ofannular form disposed in operative relation to said voice coil-adjacentthe periphery of said diaphragm so that the apex of said conical centralarea is unobstructed thereby, a permanent magnet for sup plying apolarizing force to said voice coil, said electromagnetic pole meansbeing mutually spaced by said permanent magnet so as to form a chambertherewith, said chamber being of a depth substantially equal to theheight ofthe conical central area, and annular transformer means forsupplying audio signals disposed within said chamber and electricallyconnected to said voice coil.

JOHN J. ROOT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 306,839 Great Britain Sept. 25, 1930

